1. Field of the Invention
The present invention relates to an illumination apparatus for assuring to assure illuminance uniformity and an exposure apparatus using the illumination apparatus.
2. Related Background Art
Illumination apparatus having especially strict illuminance uniformity are employed in fabricating semiconductor devices, and particularly in fabricating highly integrated semiconductor devices, such as VLSI semiconductor devices. One of the methods for improving the illuminance uniformity is for example the method as suggested in Japanese Laid-open Patent Application No. 64-42821. The method employs such an arrangement that a plane-parallel, transparent member has a shielding portion for partially interrupting a beam incident into at least one of the small lens elements in a fly's eye integrator and the plane-parallel, transparent member is located a certain distance apart from the fly's eye integrator at the incident beam side thereof.
This method realizes a distribution of uniform illuminance on a surface to be illuminated by interrupting a part of beam incident into at least one lens element among a plurality of lens elements constituting the fly's eye integrator. By interrupting a part of beam incident into a small lens element in the fly's eye integrator, an amount of correction of illuminance unevenness is about 2% to 3%. It was, therefore, almost impossible that the illuminance adjustment by this method could achieve an illuminance distribution with 1% or less illuminance unevenness.